Although disk subsystems are becoming increasingly resistant to hardware failures, regular system backups are still necessary since such failures are only one reason for performing storage and/or recovery of data. Unfortunately, backups can contribute to a large percentage of the time of a traditional batch window. Moreover, while the backup process is simple and well defined, it often requires a large amount of resources from input/output (I/O) subsystems.
In IBM MVS systems, such backups are traditionally stored on a tape medium. With the ever increasing amount of disk space and the ever decreasing size of batch windows, there is a need to be able to maximize the throughput of tape subsystems in order to move large quantities of data from disk to tape in an ever decreasing time frame.
This need can be at least partially met by using more high speed tape storage devices. However, this then creates a problem concerning management of the sheer number of tape cartridges that result. For example, to backup 1TB of data onto traditional high speed tapes requires about 500 cartridges, assuming 100% usage of all cartridges.
Recently, however, tape subsystems have been developed having markedly improved capacity. For example, the StorageTek REDWOOD device has a capacity 50 times that of prior tape subsystems, and two to four times that of a single disk storage device. It is thus capable of storing the above data on just 10 cartridges. Significantly, the StorageTek REDWOOD tape subsystem is also capable of transferring data at around 12 MB per second, while disk subsystems are capable of transferring data at around 4.5 MB per second per device (physical or logical).
Given the increased speed and capacity of such a tape subsystem, a need now exists for an easy and efficient method and system for storing data onto such a subsystem. Once the data has been placed on tape, there is also a need to reduce the physical and logical management of the data.
Current methods and systems for storing data on tape in an IBM MVS system, however, provide little ability to manage the placement and organization of the data and/or the medium. Such methods and systems involve changing the JCL for the backups to form them into fixed streams that stack the individual backups onto the media by specifying a physical position for the data on a tape volume. However, the data files must be written in sequence and further processing is required to move the data from either a disk buffer or from the original tape volume, making such methods and systems difficult to manage.
Thus, such methods and systems are incapable of direct storage and retrieval of data to and from a tape medium. This is particularly true where the data source is an application program or a system utility. Similarly, tape storage methods and systems for use in other operating systems (e.g., UNIX) are incapable of interfacing with application programs and/or system utilities.
Still further, IBM MVS based methods and systems for data storage on tape also fail to overcome the large disparity in data transfer rates between current disk devices and the tape device discussed above. In that regard, the data management principals employed dictate that one disk device is backed up to one tape device. Individual streams used are therefore only able to deliver about 25% of the performance of which the StorageTek REDWOOD tape subsystem is capable. As a result, the improved data movement capacity is vastly oversubscribed in relation to the throughput requirements of existing disk subsystems.
In short, the increased speed and capacity of the recently developed tape subsystem described above are capable of reducing processing times for backups as well as the physical media requirements for storing the data. At present, however, this capability can only be partially met by vast overcapacity of the tape systems and difficult job management.
As a result, there exists a need for a method and system capable of exploiting the increased speed and capacity of recently developed tape subsystems. Such a method and system would solve the problems discussed above by providing an extra level of data management when accessing tape. In contrast to the prior art, such a method and system would also be capable of interfacing with application programs and/or system utilities to provide direct storage and retrieval of data from such programs and/or utilities to and from a tape medium.